This invention relates to railway tank cars and, in particular, is directed to manifolded tank cars which have a novel valve and conduit system to facilitate loading and unloading of said tank cars.
The provision of fluid communication among interconnected tank cars in a railway train of tank cars is known. U.S. Pat. No. 3,897,807 discloses basically four different piping systems for tank cars which may be characterized as follows: (1) series flow, top load and unload; (2) series flow, top load and bottom unload; (3) parallel flow, top load, bottom unload with parallel top vapour vent; and (4) series flow, centre load and unload.
U.S. Pat. No. 4,007,766 discloses another system which could be categorized as (5) series flow, top load and unload with parallel vapour vent collection. Also, U.S. Pat. No. 4,008,739 discloses a system which is (6) series flow, top or bottom load and unload. U.S. Pat. No. 3,675,670 discloses another arrangement of system(1) above, i.e. series flow, top load and unload.
The system of the present invention differs from the foregoing systems and may be categorized as (7) automatic sequential flow, top load with top or bottom unload.
Some of the essential differences between the present system and conventional systems are as follows. All of the known series and parallel flow arrangements limit the loading pressure by the rated working pressure of the tank car. This pressure normally is about 60-75 psig for a conventional car and can only be increased by special design and strengthening of the car. The series flow systems are particularly limited by the rated working pressure of the tank car since all tank cars, including loaded tank cars, form an integral part of the liquid flow path. However, the automatic sequential flow of liquid permitted by the present invention by-passes each loaded car. For this reason the pressure at the loading station may be increased as successive cars are loaded so that a more constant rate of flow and hence faster loading time can be attained.
The resistance to flow of piping for known series flow systems during unloading is greater than that of automatic sequential unloading according to the present invention. The tank cars according to the present system do not form an integral part of the flow path and, hence, automatic sequential flow substantially increases unloading flow rates with similar sized conduits and air or inert gas pressure driving forces.
Known series flow systems for loading and unloading form a single point have declining flow rates and hence practical limits to the number of cars which may be connected. Automatic sequential flow allows much larger numbers of cars to be coupled in a string. This advantage allows much greater flexibility of train configuration and is adaptable to many different track layouts.
The valves in known systems do not operate sequentially but are all either in the open or closed position. For this reason, the operator cannot tell how far a loading or unloading operation has progressed until it is finished. With automatic sequential flow, the operator can observe the progress of the operation by noting the position of valve indicator flags at the cars which will tell him which car is in the process of loading or unloading.
If valves fail to operate in a series flow system, the operation must stop until the problem is remedied. However, with automatic sequential flow, other cars normally can continue to load or discharge automatically while any valve problems are being corrected.
In some circumstances, tank cars must be short loaded because of gross car weight limitations and known systems cannot achieve this without modification of the internal piping. The automatic sequential system can accomplish this simply by locating an auxiliary level switch at the appropriate level in the car.
The cost of a surge tank for pump protection at unloading sites can be saved by adapting the final car in an automatic sequential system to perform this function.
In that a train of automatic sequential tank cars may be quite long and need not necessarily be broken at the loading/unloading sites, it is adaptable to a special system which could include a loading/unloading pump and instrument control and purge apparatus on a separate car which forms part of the unit train. Such a completely self-sufficient train would be of value to users who do not wish to invest in costly loading/unloading equipment.